A vehicle may be equipped with an exhaust gas recirculation system (EGR system). The EGR system is to reduce emission contained in exhaust gas discharged from an internal combustion engine. The EGR system may recirculate a part of exhaust gas into fresh air to produce mixture gas containing recirculated exhaust gas and fresh air. Recirculated exhaust gas may be unevenly mixed with fresh air to reduce combustion efficiency of the engine consequently.